Yalantis/uCrop · error · CImgArgumentException

save_rgb(): Specified filename is (null).

Error message

save_rgb(): Specified filename is (null).

What it means

Raised by _save_rgb()'s guard when both the FILE* and filename arguments are null, meaning no output destination was specified for the RGB data (the library prints the missing filename as '(null)'). It is a generic validation check that fires before any bytes are written; give the call a valid filename or open stream.

Solutions

1. Pass a non-null filename to save_rgb()
2. Pass a valid opened FILE* instead of a null one
3. Validate the destination path/FILE* before invoking save_rgb()

Example fix

// before
img.save_rgb(name ? name.c_str() : NULL);
// after
if (name.empty()) throw std::invalid_argument("rgb output path required");
img.save_rgb(name.c_str());

if (!file && (!filename || !*filename)) throw std::invalid_argument("save_rgb requires a filename or FILE*");

bool hasDestination(std::FILE *f, const char *name) { return f != NULL || (name != NULL && name[0] != '\0'); }

try { img.save_rgb(path.c_str()); } catch (CImgArgumentException &e) { /* handle */ }

When it happens

Trigger: Calling save_rgb((std::FILE*)0); passing a null FILE* from a failed fopen; generic save() dispatch reaching the rgb path with a null name.

Common situations: Unchecked fopen result in raw-dump utilities; empty filename variables in batch conversion scripts; incorrect overload selection passing 0 as filename.

Related errors

• save_pfm(): Specified filename is (null).
• save_pnk(): Specified filename is (null).
• save_pnm(): Specified filename is (null).
• save_rgba(): Specified filename is (null).
• load_cimg(): Specified filename is (null).

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/6554779426a77a82. Report an issue: GitHub.

Appendix: source

Thrown at ucrop/src/main/jni/CImg.h:62569

      return *this;
    }

    //! Save image as a RGB file.
    /**
      \param filename Filename, as a C-string.
    **/
    const CImg<T>& save_rgb(const char *const filename) const {
      return _save_rgb(0,filename);
    }

    //! Save image as a RGB file \overloading.
    const CImg<T>& save_rgb(std::FILE *const file) const {
      return _save_rgb(file,0);
    }

    const CImg<T>& _save_rgb(std::FILE *const file, const char *const filename) const {
      if (!file && !filename)
        throw CImgArgumentException(_cimg_instance
                                    "save_rgb(): Specified filename is (null).",
                                    cimg_instance);
      if (is_empty()) { cimg::fempty(file,filename); return *this; }
      if (_spectrum!=3)
        cimg::warn(_cimg_instance
                   "save_rgb(): image instance has not exactly 3 channels, for file '%s'.",
                   cimg_instance,
                   filename?filename:"(FILE*)");

      std::FILE *const nfile = file?file:cimg::fopen(filename,"wb");
      const ulongT wh = (ulongT)_width*_height;
      unsigned char *const buffer = new unsigned char[3*wh], *nbuffer = buffer;
      const T
        *ptr1 = data(0,0,0,0),
        *ptr2 = _spectrum>1?data(0,0,0,1):0,
        *ptr3 = _spectrum>2?data(0,0,0,2):0;
      switch (_spectrum) {
      case 1 : { // Scalar image

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